1. Field of the Invention
The present invention relates to a refrigerant-transporting hose, and more specifically, to a refrigerant-transporting hose for an automobile such as an air conditioner hose or a radiator hose for transporting a refrigerant such as carbon dioxide, a chlorofluorocarbon (R12), an alternative chlorofluorocarbon (such as R-134a as a single refrigerant or Fluid H as a mixed refrigerant), or propane.
2. Description of the Related Art
A fluorine-based refrigerant such as a chlorofluorocarbon (R12) or an alternative chlorofluorocarbon (such as R-134a) has been generally used in a refrigerant-transporting hose to be used in the engine room of an automobile. In recent years, due a tightened regulation on the release of ozone layer-depleting gases, a demand on the refrigerant permeability of the refrigerant hose for an automobile has become stringent. Accordingly, a resin material having high crystallinity such as a polyamide has been used in a resin layer (innermost layer) of the refrigerant-transporting hose intended to contact the refrigerant.
However, it has been known that a refrigerant for an automobile deteriorates owing to long-term use, which generates an acid. The acid decomposes an amide bond of the polyamide. Moreover, the refrigerant-transporting hose such as an air conditioner hose for an automobile is typically used under a high-temperature environment, and hence the chemical deterioration of the polyamide by the acid is apt to be promoted. Accordingly, bending the refrigerant-transporting hose causes a problem such as cracking of the resin layer of the hose. An aliphatic polyamide such as a polyamide 6 which has been conventionally used deteriorates owing to hydrolysis. Accordingly, the aliphatic polyamide is not suited for any application of the refrigerant-transporting hose and hence its improvement has been demanded.
In recent years, a semi-aromatic polyamide such as a polyamide 9T (PA9T) has been attracting attention as a material for the refrigerant-transporting hose because the semi-aromatic polyamide is excellent in low-refrigerant permeability and acid resistance. However, the semi-aromatic polyamide involves the following problem. The semi-aromatic polyamide has high rigidity and thus poor flexibility. To solve this problem of the semi-aromatic polyamide, an approach involving mixing the PA9T as a main component with an aliphatic polyamide has been proposed in the field of a joint for fuel piping (Japanese Laid-open Patent Application No. 2004-150500).
However, even when the resin layer of the refrigerant-transporting hose is produced with the resin composition described in Japanese Laid-open Patent Application No. 2004-150500, which is obtained by mixing the PAST as a main component with the aliphatic polyamide, the problem concerning flexibility cannot be sufficiently solved and hence the improvement of the flexibility has been demanded.